The objective of this project is to study the structure and function of human gastric proteases, gastricsin and pepsin. It is proposed to elucidate the complete amino-acid sequence of these human enzymes using the general approaches we have developed for the study of the complete sequence of porcine pepsin.The active center of these human enzymes will be studied using the specific expoxide- and diazo-inactivators. These studies will hopefully be supported by a x-ray crystallographic study of human gastricsin. The physiological origin of gastric enzymes will be studied. Porcine pepsinogen will be used as a model to elucidate the zymogen activation mechanisms of gastric proteases.